Magoo,
I just saw this now and caught up with your progress. I went through the same process as you where the small layout for the kids became my obsession! I also have the M7 and decided to build an O48 elevated figure eight to run it. It allows you to separate your passenger service and not clutter up your main level. I built all the trestles with MDF and wood dowels and it was quite easy.
good luck with your expansion,
Jay in Ottawa